Documents like birth certificates in Italy are free. If you send by mail, include a self addressed envelope. From what I have read, they can't use US stamps so you can include a International Reply Coupon:

Historical certificates are rarely charged for but 26 euro cents (34 cents) is a normal charge for a certificate at the Comune anagrafe. Cost of mailing to America is 1,60 euro. Coupons and bank drafts are a waste of time. They cost more to cash in time and money than they are worth which is why they send them back. Better to send 5 euro in cash and an addressed envelope (that way you are sure it will be addressed properly).

Thanks so much for the input! Since I am pursuing dual citizenship and the documents I seek must have an apostille (official seal), will the certificates automatically come that way or should I specifically ask for the apostille?

I am not sure if the Comune's official stamp and signature will be enough. The last time I had to get an apostille stamp on a certificate I had to take it to Frosinone where they authenticated the signature. I can only assume that is what an apostille is.

I appreciate everyone's input. I actually sent two letters in the past couple of years and heard nothing. That's why I wanted to send something certified. I think I'll wait until September and send another letter.